The present disclosure relates to a fixing device used for a copy machine, a printer, a facsimile, a multifunction peripheral including these, or the like, and an image forming apparatus including the fixing device. Particularly, the present disclosure relates to a fixing device of electromagnetic induction heating type and an image forming apparatus including the same.
In image forming apparatuses of electrophotographic type, a halogen heater or the like is widely used as a heat source for a fixing device which fixes a toner image on a recording medium. Meanwhile, in recent years, there is a demand for reduction of warm-up time or energy saving. In addition, an induction heating (IH) type is known in which an alternating magnetic field is interlinked with a magnetic conductor to cause eddy current, thereby providing heating.
In the induction heating type, an induction heating coil is used. The induction heating coil is formed by winding a litz wire along the outer circumferential surface of a bobbin extending in the width direction (direction perpendicular to a sheet conveyance direction) of a heating member such as a heating roller or a fixing belt. When high-frequency current is applied to the induction heating coil, high-frequency magnetic flux occurs. The high-frequency magnetic flux acts on an induction heat generation layer of the heating roller or the fixing belt, whereby eddy current occurs around the magnetic flux of the induction heat generation layer. Thus, Joule heat due to resistance intrinsic to a material in the induction heat generation layer occurs, thereby heating the heating member such as the heating roller or the fixing belt. The fixing device of IH type enables reduction of the heat capacitance of the heating member. Therefore, warm-up time is reduced and an enhanced heat conversion efficiency is obtained with a compact configuration.
In the above IH type, there are various placement manners for the coil relative to the heating member. One of them is to place the coil outside the heating member. In one such example, the heating member is a heating roller, and an induction heating coil is wound in the rotation axis direction (longitudinal direction). In another such example, the heating member is a heating belt, and an induction heating coil is wound in the belt width direction. Hereinafter, such a configuration is referred to as an outer surrounding type (axis direction winding) coil.
Meanwhile, in order to prevent the temperature of the coil from increasing to exceed the heat resistant temperature, the fixing device of IH type may include a cooling mechanism which blows air to the coil by using a fan. For example, a fixing device of IH type is proposed which includes a cooling mechanism that causes air to pass in the longitudinal direction of the coil.
In addition, a fixing device of IH type is proposed which includes a cooling mechanism that causes air to pass in the sheet passing direction (direction perpendicular to the longitudinal direction of the coil) of a paper sheet and uses air flow having been used for cooling the coil, for separating a paper sheet at a fixing nip portion.